[I own but have not yet opened or installed, a Deco M4 system.]

A TP-Link FAQ for the Deco units states, "For some reason, if you want to change the slave Deco to work as the Main Deco but do not want to reset the whole Deco network and reconfigure it, you can refer to the following instruction to finish the setup process."

The instructions certainly go on to tell you how to do it, but what would "some reason" be?  Is there some advantage to making a slave Deco the Main Deco?  Would it get a stronger signal if it was designated the Main Deco?  I ask because when I install my system in a few days, the Main Deco will start off next to my modem, in a room where I don't require a good WiFi signal.  The place where I'll place one of the two Deco "slaves" is at the end of my house where there are several WiFi devices that would benefit from a better signal.  Obviously I'm just wondering what the benefit of changing the designations would be, if any (and I'd have to suppose there would be one or two, or why is this available to do, right?).